Usually refers to a situation where a male is "doing" a female from behind at the top of a flight of stairs. Just before ejaculating, he pushes his partner's arms out from under her, and rides her down the stairs.

A good way to get out of a bad relationship.

Man, I was doing Julie at the top of the stairs last night, and I suddenly decided to snowmobile her. It was pretty sweet.

An off-road vehicle (OAV) designed and intended for use upon snow in regions which get substantial amounts of snowfall
They have one safety mechanism and almost anyone can learn to drive one, supposing he is
a) over the age of 14 and
b) he has both hands